• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.40-47
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• 2018

Porous walkway blocks are constructed for the purpose already, but reserved water is easily consumed due to the bigger permeability than necessary. Furthermore, porous structure reduces the strength of blocks, which resulting cracking and settlements in walkways. In this study, we suggested a solution for given problems by determination for the location of minimum principal stress in walkway blocks against moving foot loads in order to design and verifying the determined location of minimum principal stress. An optimum design with a verification example for determined location of minimum principal stress have been presented in a two dimensional Block member on elastic foundation for pedestrian walkway for reserving water inside. The minimum value for sum of shear forces is found when ${\times}1$ is 58.58 mm(30% of total span, 200mm), while the minimum deformation is located at ${\times}2=80mm$(70% of total span, 200 mm). In a modified model, When moving boundary condition(walkway foot loads) is located at ${\times}1$(=0 mm), the location of minimum principal stresses is found at 168 mm( 84% of span, 200 mm), in which the stress concentration due to the foot load is modeled as two layers of distributed loads(reactions of foundation modeled as springs). Consequently, zero deformed reservoirs for rainwater on the neutral axis (${\times}2=167mm$) has been determined in the modified model with three dimensional FEM analysis verifications.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.5
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• pp.178-189
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• 2011

Tests and analyses were performed in this study to assess the shear strength of Reinforced Concrete(RC) members strengthened by the Near Surface Mounted(NSM) technique in shear, which is drawing attention as an alternative to the Carbon Fiber Reinforced Polymer(CFRP) bonding strengthening technique. Four-point bending tests were performed on 7 RC specimens without any shear reinforcement. The test variables such as the inclination of CFRP strip (45 degrees and 90 degrees), and the spacing of CFRP strip (250mm, 200mm, 150mm, 100mm) were considered. Through the testing scenarios, the effect of each test variable on the failure mode and the shear strength of the RC members strengthened by the NSM technique in shear were assessed. The test results show that the specimens with CFRP strips at 45 degrees go to failure as a result of the strip fracture, but the specimens with CFRP strips at 90 degrees go to failure as a result of the slip of strips. Strips at 45 degrees was the more effective than strips at 90 degrees, not only in terms of increasing beam shear resistance but also in assuring larger deformation capacity at beam failure. In addition, the RBSN analysis appropriately predicted the crack formation and the load-displacement response of the RC members strengthened by the NSM technique in shear.

• Journal of the Korean GEO-environmental Society
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• v.17 no.12
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• pp.27-34
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• 2016

Many steepened slopes have become increasingly advantageous because of the desire to increase land usage and decrease site development costs. The proven concept of tensile reinforcement allows construction of slopes with far steeper face angles than the soils natural angle. Steepened slope face reinforced with improved soil can increase land usage substantially while providing a natural appearance. The paper presents composite reinforced earth with improved soil surface and geogrid-reinforced backfill. For the stability of the steepened slope, the behavior of the composite reinforced earth are validated and verified by case study and numerical analysis. The case study has performed to investigate the deformation of reinforce soil slope for 14 months. Its horizontal behavior by general vertical load shows within the safe range (0.5% of structure height). As a result of numerical analysis and case study, the reinforcement effect of the steepened slope technique using improved soil is sufficient to be constructed as reinforced soil slope.

• Journal of the Korean Society for Railway
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• v.14 no.5
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• pp.433-441
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• 2011

It is a fact that the straightening of track alignment is one of the undoubted ways to improve the train speed on conventional lines, while that requires huge investment resources. Therefore, the operation of a tilting train as well as the minimum improvement of track is suggested as an effective and economical alternative way for the speed-up of conventional lines. Since a driving mechanism of tilting train is different from those of existing trains, in order to make sure its operation safety and stability on conventional line, the performance of track and roadbed must be preferentially evaluated on the conventional line. Furthermore, it is necessary to estimate the tilting-train-induced roadbed response in detail since the roadbed settlement can lead to the track deformation and even derailment. In this research, the patterns of wheel load and lateral force were monitored and analyzed through the field tests, and the derailment coefficient and degree of wheel off-loading were calculated in order to evaluate the tilting train running safety depending on the running speeds (120km~180km) on the conventional line. Moreover, roadbed pressure, settlement and acceleration were also observed as tilting-train-induced roadbed responses in order to estimate the roadbed stability depending on the running speeds. Consequently, the measured derailment coefficient and degree of wheel off-loading were satisfied with their own required limits, and all of the roadbed responses were less than those of existing high-speed train (KTX) over an entire running speed range considered in this study. As a result of this study, the tilting train which will be operated in combination with existing trains is expected to give no adverse impact on the conventional line even with its improved running speed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1438-1443
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• 2001

The significance of the casting/forging process for reducing the production cost of large components is being noted in these days. This casting/forging process is a method of forging a workpiece preformed by casting into the final shape. In this study, the casting/forging process has been applied in manufacturing a large aluminum flange in order to reduce press capacity and material cost. Firstly, a hot compression test was performed with cast cylindrical billets in order to determine the optimum forging condition of the aluminum flange. The optimum range of forging temperature of Al 5083 was from 420$\^{C}$ to 450$\^{C}$. The suitable strain rate was 1.5 sec(sup)-1. The deformation amount of a preform of a preform in a forging process is a key role in the mechanical properties of casting/forging products. In order to find the change of mechanical properties according to effective stain of cast aluminum billets, a hot upsetting test were performed with rectangular blocks and then a uniaxial tensile test was performed with specimens cut from the upsetted billets. The tensile strength and the elongation of cast/upsetted aluminum billets were increased largely until the effective strain was 0.7. FE analysis was performed to determine the configurations of case preform and die for an aluminum flange. In the FE analysis, the forging load-limit was fixed 1500ton for low equipment cost. The cast preform was designed so that the effective stain around the neck of a flange exceeded 0.7. From the result of FE analysis, optimal configurations of the cast preform and the die were designed for a large flange. The filling and solidification analysis for a sound cast-preform was carried out with MAGMA soft. In the forging experiment for an aluminum flange, it was confirmed that the optimal configuration of the cast preform predicted by FE analysis was very useful. The cast/forged products using designed preform were made perfectly without any defects.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.103-113
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• 2015

This paper studies impact performance of wire-mesh and steel fiber-reinforced concrete based on high-velocity impact experiments using hard spherical balls. In this experimental study, panel specimens were tested with various parameters such as steel fiber volume fraction, presence/absence of wire mesh, panel thickness, impact velocity, and aggregate size for the comparison of impact resistance performance for each specimen. While improvement of the impact resistance for reducing the penetration depth is barely affected with steel fiber volume fraction, the impact resistance to scabbing and perforation is improved substantially. This was due to the fact that the steel fiber had bridging effects in concrete matrix. The wire mesh helped minimizing the crater diameter of front and back face and enhanced the impact resistance to scabbing and perforation; however, the wire mesh did not affect the penetration depth. The wire mesh also reduced the bending deformation of the specimen with wire mesh, though some specimens had splitting bond failure on the rear face. Additionally, use of 20 mm aggregates is superior to 8 mm aggregates in terms of penetration depth, but for reducing the crater diameter on front and back faces, the use of 8 mm aggregates would be more efficient.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.5
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• pp.527-533
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• 1999

Hertzian indentation tests with spherical indenters in water were conducted to examine the contact fatigue in three dental ceramics, such as feldspathic porcelain, micaceous glass-ceramic (MGC) and glass-infiltrated alumina, which was used as dental restorations, and evaluated the effect of contact damage on strength. Initial damage was dependent of microstructure, showing cone cracks of brittle behavior in the feldspathic porcelain and deformation of quasi-plastic behavior in the MGC, with an intermediate case in the glass-infiltrated alumina. However, as increasing the number of cyclic loading (n=1~n =$10^6$)all materials showed an abrupt strength degradation, at which fracture was originated from damage in the contact fatigue. There were two strength degradation with increasing the number of cyclic loading in specific loads (200N, 500N, 1000N):first was from the cone cracks, and second was from the radial cracks created by cyclic loading. The radial cracks, once formed, led to rapid degradation in strength properties, Finally the material was failed at the high number of cyclic loading. Strength degradation with indentation load at fixed number of cyclic loading indicated that the feldspathic porcelain should be highly damage tolerant to the contact fatigue.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.12
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• pp.2351-2357
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• 2008

Noninvasive radial artery pulse wave has been widely used not only for the pulse wave analysis(PWA) itself but also for assessment of arterial stiffness with estimated aortic pulse wave from peripheral pulse wave. However, it has been found that the deformation of pulse shape can be caused readily by changing measuring position, indentation pressure, and so on. So, in this study, we have developed a system which can measure radial pulse wave and skin displacement simultaneously while the indentation body goes down to occlude subject's radial artery. This system can be divided into a measuring apparatus part, an indentation control hardware part, a data acquisition part and a control and computation part. And, the measuring apparatus consists of an arm-rest, a step motor, an indentation body, a laser displacement sensor(LK-G30, Keyence Co.) and pulse wave sensor. Under load-free condition and radial artery loaded condition, the evaluation of developed system has been performed. From these results, we can conclude: 1) The developed system can control the indentation body quantitatively and the adopted laser displacement sensor shows linear output characteristic even with skin as a reflector. 2) This system can measure the pulse wave and the displacement of indentation body, that is, skin displacement simultaneously at each specific level of indentation body. 3) This system can provide the number of motor steps used to get down the indentation body, the measured skin displacement, the calculated indentation pressure, the calculated pulse pressure and the pulse waveform as well as the information generated by combining these with each others. 4) This system can reveal the relationship between the morphological changes of pulse wave and the estimated displacement of radial artery wall by indentation. Consequently, the developed system can furnish more abundant information on radial artery than previous diagnosis systems based on tonometric measurement. In further study, we expect to setup the standard measuring process and to concrete the algorithm for the estimation of radial artery's diameter and of displacement of radial artery's wall. Furthermore, with well designed clinical studies, we hope to turn out the usefulness of developed system in the field of cardiovascular system evaluation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.491-499
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• 2002

A p-version finite element model based on degenerate shell element is proposed tot the analysis of orthotropic laminated plates. In the nonlinear formulation of the model, the total Lagrangian formulation is adopted with large deflection and moderate rotation being accounted tot in the sense of yon Karman hypothesis. The material model is based on the Huber-Mises yield criterion and Prandtl-Reuss flow rule in accordance with the theory of strain hardening yield function, which is generalized lot anisotropic materials by introducing the parameters of anisotropy. The model is also based on extension of equivalent-single layer laminate theory(ESL theory) with shear deformation, leading to continuous shear strain at the interface of two layers. The integrals of Legendre polynomials are used for shape functions with p-level varying from 1 to 10. Gauss-Lobatto numerical quadrature is used to calculate the stresses at the nodal points instead of Gauss points. The validity of the proposed P-version finite element model is demonstrated through several comparative points of iew in terms of ultimate load, convergence characteristics, nonlinear effect, and shape of plastic tone.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.489-494
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• 2015

This research focused on minimizing the response of fixed cylindrical offshore structures to a ship impact considering the seawater fluid part. A collision between a ship and offshore structure is generally a complex problem and it is often impractical to perform rigorous finite element analyses to include all the effects and sequences during the collision. The structural behavior of a fixed cylindrical type offshore substructure with a seawater fluid part has a simpler response and small deformation due to the dissipation of impact energy. Upon applying the impact force of a ship to the cylindrical structure, the maximum acceleration, internal energy, and plastic strain are calculated for each load cases using Ls-dyna finite element software. In the maximum cases 2.0 m/s velocity, the response result for the structure was carried out to compare between having a fluid region and no fluid region. Fluid-structure interaction analysis was performed using the ALE method, which make it possible to apply a fluid region on the impact problem. The case of a fixed cylindrical type offshore structure without a seawater fluid part can be a more conservative design.